METHODS AND COMPOSITIONS FOR MODULATING LIPID CONTENT OF PLANT TISSUES

Abstract: Novel compositions and methods are provided for modifying the lipid content of plant tissues of interest, including leaf, root, fruit and seed. The methods involve transforming a plant cell of interest with an expression cassette functional in a plant cell comprising a transcriptional and translational initiation regulatory region, joined in reading frame 5' to a DNA sequence encoding an enzyme capable of modulating the production of fatty acids, and translational and transcriptional termination regions. Expression of the enzyme provides for an increase in fatty acid biosynthesis as a result of altered concentrations of substrate for enzymes involved in fatty acid biosynthesis. Of particular interest is the selective control of lipid production in plant tissues such as leaves, root, fruit and seed.

Description: METHODS AND COMPOSITIONS FOR MODULATING LIPID CONTENT OF PLANT TISSUES INTRODUCTION Fie.1^ of the Invention This invention relates to modulating levels of enzymes and/or enzyme components capable of increasing the amount of malonyl-CoA in plant cells. Background It is of value in some oilseed crops to increase the lipid content in seed. One means to do so is to increase the rate of fatty acid biosynthesis during storage lipid deposition by some application of genetic engineering technology. However, an exact approach has not been defined or demonstrated even though there have been many possibilities proposed. Malonyl-CoA is an essential metabolite for several biosynthetic pathways in plants. One pathway for its formation is through the action of acetyl- CoA carboxylase (ACC) (EC 6.4.1.2) on acetyl-CoA and bicarbonate: ACC catalyzes the ATP-dependent carboxylation of acetyl-CoA to malonyl-CoA. In plants, malonyl-CoA is a common intermediate in fatty acid biosynthesis and in the pathway leading to the biosynthesis of cuticular waxes, flavonoids, anthroquinones, N-malonyl-ACC and malonic acid. In yeast and animal cells, ACC has a rate-limiting role in fatty acid biosynthesis. ACC has been hypothesized to be the rate-limiting step for fatty acid biosynthesis in plants. It therefore is of interest to evaluate the role of ACC carboxylase in fatty acid biosynthesis in plants, as a means of developing methods and compositions for altering the lipid content of plant tissues. Relevant Literature Verwoert and coworkers (Verwoert et al , (1992) Dept. of -Genetics 424-427) cloned the E. colifabO gene encoding malonyl-CoA:ACP transacylase (MTA) and modified it for seed-specific expression. They reported high-level, seed-specific expression of MTA in several plants (rape, petunia, and tobacco) but no significant change was observed in the fatty acid composition or content of the seed. Although ACC has been suggested as a rate-limiting step for fatty acid biosynthesis in developing seed based on data of Turnham and Northcote, (1983) Biochem. J. 212:223-229, the evidence is circumstantial. In vivo studies indicate that fatty acid biosynthesis is a highly regulated pathway; fatty acid biosynthesis in leaves is five-fold higher in the light than in the dark Post-Beittenmiller et al. , (1991) J. Biol. Chem. 26^: 1858-1865). Analysis of in vivo pools of acyl-ACP intermediates in these leaf tissues indicated that the ACC-catalyzed reaction is far from equilibrium and thus potentially a rate-limiting step in the pathway (Post- Beittenmiller et al , (1991) supra. ACC enzymes from E. coli, from yeast (Al-Feel et al , (1992) Proc. Natl. Acad. USA 22:4534-4538), and from animal cells (rat liver) (Lopez-Castillas et al , (1988) Natl. Acad. Sci. USA 8^:5784-5788) are relatively well characterized; complete primary structures deduced from cloned genes are available. Animal and yeast ACC enzymes have all the functional peptide units of ACC (biotin carboxylase, BC); (carboxyl carrier protein, BCCP); (transcarboxylase, TC) assembled into one comparatively large multifunctional protein encoded by a single gene Al-Feel et al. , (1992) Proc. Natl. Acad. USA 52:4534-4538; Lopez-Castillas et al. , (1988) Proc. Natl Acad. Sci. USA 35:5784- 5788 whereas in prokaryotes the function of units of ACC are separate. The structure of ACC in plants is less clear. ACC enzyme from wheat germ, parsley suspension cultures, and rape seed and leaf is composed of a single high molecular weight polypeptide of approximately 200-240kDa (e.g., Slabas and Hellyer, (1985) Plant Sci. 22: 177-182; Slabas et al > (1986) Soc. Trans. Lond. 14:716; Εgin-Buhler and Εbel, 1983) Eur. J. Biochem. 13 : 335-339). However, Kannangara and Stumpf, (1972) Archives of Biochem. and Biophys. 152:83-91 demonstrated that the spinach ACC isolated from disrupted chloroplasts can be resolved in two activities: BC found with BCCP in lamellar fractions, and TC found in the stroma. Whether the enzyme in vivo may actually be a single peptide is still not known. However, a protein fraction containing an E. coli TC could replace the TC fraction from spinach chloroplast extracts in an in vitro assay system when combined with the fraction containing plant "BCCP" and plant "biotin carboxylase" (Kannangara and Stumpf, 1972). Moreover, an E. coli extract containing BC and BCCP exhibited ACC activity when combined with a plant extract containing TC activity. Although these in vitro data suggest the possibility that an E. coli ACC subunit might contribute some functional role to plant ACC in vivo, the experiments did not establish whether plant BC could interact functionally with an E. coli BCCP. Summary of the Invention Novel compositions and methods are provided for modifying the malonyl-CoA dependent biosynthetic pathways, particularly to modify lipid levels, in plant tissues of interest. The methods involve transforming a plant cell of interest with an expression cassette functional in a plant cell comprising a transcriptional and translational initiation regulatory region, joined in reading frame 5' to a DNA sequence encoding an ACC component capable of modulating the production of malonyl-CoA, and translational and transcriptional termination regions. Expression of the ACC component provides for an increase in lipid production as a result of altered concentrations of malonyl-CoA for enzymes involved in lipid biosynthesis. Of particular interest is the selective control of lipid production in plant tissues such as leaves, roots, fruits and seeds. Brief Description of the Drawings Figure 1 shows the construction of pCGN3989, pCGN3992, and pCGN3993. The accB coding region was amplified by polymerase chain reaction (PCR) using synthetic DNA primers which place a BamHl recognition sequence immediately upstream of the accB initial ATG codon and a Sacl recognition sequence just downstream of the translational stop codon. The αccB coding region was then excised from pCGN3988 as a BamUl-Sacl fragment which was directly subcloned into pCGN2187 to create pCGN3989 (see Figure 2, pCGN2187). In the case of pCGN3992, a BamKl fragment was subsequently added to pCGN3989 to create a sequence encoding a fusion protein containing the chloroplast transit region of ribulose bisphosphate carboxylase (RUBISCO) plus the first six amino acids of mature RUBISCO. In the case of ρCGN3993, the added BanϊΑ fragment encoded the complete transit region plus 12 amino terminal amino acid residues of mature RUBISCO. Figure 2 shows the composition of pCGN2187. The promoter region, entitled double 35S or d35S, contains bases -363 to -90 of the cauliflower mosaic virus (CaMV) genome (Gardner et al, (1981) Nucl. Acids Res. 2:2871-2888) fused to bases -941 to +112 of the CaMV genome. The transcription terminator region is derived from bases 11207 to 10069 of the octopine Ti Plasmid pTiA6 using the numbering system of Barker et al. , (1983) Plant Mol. Biol. 2:335-350. The terminator region corresponds to the functional counterpart of a "tml" gene in the Agrobacterium T-DNA and is thus termed tml. Figure 3 (pCGN3916): 3077 bases of E. coli strain mm294 chromosome containing the αccB and accC genes. Translation from bases 800- 1267 represent the preprotein of BCCP; 1281-2627 the BC enzyme. Figure 4 (pCGN3933): 3231 bases of Pseudomonas aeruginosa strain PaO chromosome containing the accB and accC genes. Translation from bases 861-1331 represent the preprotein of BCCP; 1349-2698 the BC enzyme. Description of the Preferred Embodiments In accordance with the subject invention, novel DNA sequences, DNA constructs, methods and compositions are provided which permit modification of the lipid content of plant products by means of increased production of a substrate for lipid biosynthesis, malonyl-CoA (MCA), in a tissue of interest. Plant cells are transformed with an expression cassette comprising a DNA encoding an ACC polypeptide capable of increasing the amount of malonyl-CoA in the tissue of interest. Desirably, integration constructs may be prepared which provide for integration of the expression cassette into the genome of a plant host. Depending upon the desired application, the ACC polypeptide can be preferentially expressed in a tissue of interest and/or a particular organelle. Tissue specificity is accomplished by the use of transcriptional regulatory regions having the desired expression profile. Translocation of the enzyme to a particular organelle is accomplished by the use of an appropriate translocation peptide. To provide for an increased level of lipid in a plant, a plant cell is transformed with an expression cassette which includes as operably linked components in the 5'-3' direction of transcription, a transcriptional and translation initiation region, a structural gene encoding an ACC polypeptide capable of increasing levels of malonyl-CoA, and a transcriptional and translational termination regulatory region. For organelle targeting, a DNA sequence encoding a transit peptide and processing signal is included. Expression in plant tissue cytoplasm may be sufficient to modulate lipid biosynthesis pathways found outside of plastid organelles. The initiation and termination regulatory regions are functional in the host plant cell and may be either homologous or heterologous to the host plant and to the structural gene. Of particular interest as a means of increasing malonyl-CoA concentration is use of an ACC polypeptide which is capable of metabolizing malonyl-CoA from substrates normally found in plant cell. Particularly of interest is an ACC polypeptide which acts on the malonyl-CoA precursors for the desired end use. By ACC polypeptide is intended a polypeptide which contributes to the conversion of acetyl-CoA to malonyl-CoA. By polypeptide is meant any chain of amino acids, regardless of length or post-translational modification (e.g. glycosylation or phosphorylation). The polypeptide may be a component subunit of ACC carboxylase, for example BCCP, TC, or BC, or any combination of subunits, including the entire carboxylase enzyme. The polypeptide can also be any portion of a subunit alone or in combination with other subunits. Considerations for use of a specific ACC polypeptide in plant tissue for the production of precursors of malonyl-CoA biosynthesis include pH optimum of the polypeptide, whether the ACC polypeptide is a rate-limiting enzyme or a component thereof, i.e., the product of the enzyme used is essential for fatty acid biosynthesis, and co-factors required by the polypeptide. The ACC polypeptide should have kinetic parameters compatible with the biochemical environment found in the host plant cell. For example, the polypeptide may have to compete for substrate with other enzymes. Analysis of the K m and specific activity of the polypeptide in question therefore should be considered in determining the suitability of a given polypeptide for increasing malonyl-CoA production in a given host plant. The polypeptide thus is one which can function under conditions present in the desired target tissue, but otherwise can be any ACC polypeptide having the desired characteristic of being capable of positively increasing the production of malonyl-CoA. Of interest as a source of an ACC polypeptide is a component of an enzyme which produces MCA, particularly E. coli ACC. The E. coli ACC enzyme can be separated into four subunits: biotin carboxyl carrier protein (BCCP), a dimer of two 22.5 kDa subunits, biotin carboxylase (BC), composed of two 51 kDa subunits, and transcarboxylase (TC), composed of two 30 kDa subunits and two 35 kDa subunits (Alberts and Vagelos, (1972) p. 37-82. In P.D. Boyer (ed), The Enzymes, 3rd ed., Vol. 6. Academic Press, New York). The four genes that specify the individual subunits of the E. coli enzyme have been cloned and their nucleic acid sequences have been determined: accB(fabB) Muramatsu and Mizuno, (1989) Nucleic Acids Res. 17:3982 and accC (fabG) Kondo et al. , (1991) Proc. Natl. Acad. Sci. USA ££:9730-9733 encode the BCCP and BC subunits respectively, and acck and accD (dedB) encode the or and β subunit of the TC protein (Li and Cronan, (1992) J. Biol Chem. 26.7: 16841-16847). These genes can be individually expressed in transgenic plants to effect greater synthesis of MCA. Other sources of ACC subunits substantially identical to the E. coli subunits also can be used. By "substantially identical" is meant an amino acid or nucleic acid sequence exhibiting at least 60%, preferably 80%, more preferably 90%, and most preferably 95 % homology to a reference amino acid or nucleic acid sequence. For polypeptides, the length of comparison sequences will generally be at least 16 amino acids, preferably at least 20 amino acids, or preferably at least 25 amino acids, and most preferably 35 amino acids. For nucleic acids, the length of comparison sequences generally will be at least 50 nucleotides, preferably at least 60 nucleotides, more preferably at least 75 nucleotides, and most preferably 110 nucleotides. Homology typically is measured using sequence analysis software (for example, sequence analysis software package of the Genetics Computer Group, University of Wisconsin Biotechnology Center, 1710 University Avenue, Madison WI 53705). Such software matches similar sequences by assigning degrees of homology to various substitutions, deletions and other modifications. Conservative substitutions typically include substitutions within the following groups: glycine and alanine; valine, isoleucine and leucine; aspartic acid glutamic acid, asparagine and glutamine; serine and threonine; lysine and arginine; and phenylalanine and tyrosine. For the most part, some or all of the coding sequence for the ACC polypeptide will be from a natural source, and the structural gene which is a source for DNA encoding the ACC polypeptide can be obtained in a variety of ways. It can be obtained various prokaryotic cells as well as from various eukaryotic cells: both eukaryotic and prokaryotic cells are capable of producing MCA. ACC polypeptide is obtainable from E. coli and from other prokaryotic ACC enzymes such as Pseudomas aeruginosa ACC enzyme and Bacillus subtilis ACC enzyme. Plant chloroplast ACC may consist of discrete subunits such as are found in E. coli, and thus resemble a prokaryotic enzyme structure. Plant chloroplast ACC therefore may also be a source of ACC polypeptide. For example, several diverse plants contain within their chloroplastic genomes certain DNA sequences, exemplified by the pea zpfk, which possibly encode proteins sharing homology with the β subunit of the E. coli TC protein (Li and Cronan, (1992) Plant Molec. Biol 2Q:759-761). In some situations it may be desirable to modify all or a portion of the codons, for example to enhance expression, by employing host-preferred codons. Methods for identifying sequences of interest have found extensive exemplication in the literature, although in individual situations, different degrees of difficulty may be encountered. Various techniques include the use of probes where genomic or cDNA libraries may be searched for complementary sequences. The coding sequence for the ACC polypeptide may be synthesized in whole or in part, particularly where it is desirable to provide plant preferred codons. Thus, all or a - 1 - 467 portion of the open reading frame may be synthesized using codons preferred by the plant host. Plant preferred codons may be determined from the codons of highest frequency in the proteins expressed in the largest amount in the particular plant species of interest. Methods for synthesizing sequences and bringing the sequences together are well established in the literature. Where a portion of the open reading frame is synthesized, and a portion is derived from natural sources, the synthesized portion may serve as a bridge between two naturally occurring portions, or may provide a 3'-terminus or a 5'- teπninus. Particularly where a leader sequence is used and the open reading frame encoding the ACC polypeptide and the leader sequence are derived from different genes, synthetic adapters commonly will be employed. In other instances, polylinkers can be employed, where the various fragments can be inserted at different restriction sites or substituted for a sequence in the polylinker. In vitro mutagenesis and selection, site-directed mutagenesis, or other means may be employed to obtain mutations of naturally occurring ACC genes to produce an ACC polypeptide with activity in vivo with more desirable physical and kinetic parameters for function in the plant cell, such as a higher rate of production of MCA. If the ACC polypeptide coding sequence is from a prokaryotic source, in order to have expression of the gene in a plant cell, transcriptional and translational initiation regulatory regions or promoters functional in plant cells must be provided operably linked to the coding sequence. Transcription and translation initiation signals functional in plant cells include those from genes which are present in the plant host or other plant species, and direct a fairly uniform or constitutive expression in a plant host, for example those present in viruses such as the cauliflower mosaic virus (CaMV), for example the 35S transcriptional initiation region and those associated with T-DNA such as the opine synthase transcriptional initiation regions, for example, octopine, mannopine, agropine, etc. The transcription and translation initiation regions may be obtained from the same or different 5' non-coding upstream regulatory region(s). Of particular interest is a transcriptional initiation region in a construct comprising two 35S promoters in tandem (also referred to as a "Double 35S" promoter), mannopine synthase/35S promoter constructs (See, USPN 5,106,739 issued April 21, 1992 and Comai, et al , Plant Mol. BioL, (1990) 11:373-381), 34S promoters (See, USSN 404,283 filed September 7, 1989 and Sanger, et al , Plant Mol. Bio. , (1990) H:433-443). By "promoter" is intended a sequence sufficient to direct transcription. Also included are those promoter elements which are sufficient to render tissue- specific gene expression; such elements may be located in the 5' or 3' regions of a native gene. By "operably linked" is meant that a gene and a regulatory sequencers) are connected in such a way so as to permit gene expression when the appropriate molecules (for example, transcriptional activator proteins) are bound to the regulatory sequence(s). By "plant cell" is meant any self-propagating cell bounded by a semi-permeable membrane and containing a plastid. Such a cell also requires a cell wall if further propagation is desired. Plant cell, as used herein, includes without limitation, seeds, suspension cultures, embryos, meristematic regions, callous tissue, leaves, roots, shoots, gametophytes, sporophytes, pollen, and microspones. Depending upon the application, promoters also may be obtained from genomic clones of cDNAs which demonstrate preferential expression according to a specific tissue and/or timing profile. For example, leaf specific cDNAs (Dunsmuir, et al. Nucleic Acids Res. (1983) 11:4177-4183), root tips (Pokalsky, et al. Nucleic Acids Res. , (1989) 17:4661-4673), and fruit (Peat et al. Plant Mol. Bio , (1989) 13_:639-651) and the like can be employed. Within such classes of promoters, further differentiation may be observed between more generalized tissue specific promoters and very localized or timing specific promoters. For example, promoters showing differential expression patterns in fruit are described in USPN 4,943,674, issued July 24, 1990 and in co-pending applications USSN 582,241 , filed September 14, 1990 (also WO-A 8 809 334), USPN 5, 175,095 issued December 29, 1992 (also EP-A 0 409 629), and USSN 555,711, filed July 19, 1990 (also EP-A 0 409 625). Depending upon the specific application, a promoter is chosen which provides the desired expression pattern. Promoters demonstrating preferential transcriptional activity in plant tissues are described in USSN 742, 834, filed August 8, 1991 (also EP-A 0 255 378) and USSN 494, 722 (also WO-A 9 113,980). Other promoters from genes which have a differential pattern of expression in a specific tissue can be identified by differential screening of a tissue of interest, using methods described for example in USPN 4,943,674 and EP-A 0255378. The regulatory regions may be homologous (derived from the plant host species) or heterologous (derived from source foreign to the plant host species), to the plant host or a synthetic DNA sequence. The term "homologous" includes both indigenous and endogenous sequences. In order to join the promoter(s) to the structural gene, the non-coding 5' region upstream from the structural gene may be removed by endonuclease restriction. Alternatively, where a convenient restriction site is present near the 5' terminus of the structural gene, the gene can be restricted and an adapter employed for linking the structural gene to a promoter region, where the adapter provides for any lost nucleotides of the structural gene. The termination region can be derived from the 3 '-region of the gene from which the initiation region was obtained or from a different gene. The termination region can be derived from a plant gene, particularly from the same plant gene used as a source of sequences to initiate transcription and translation. Other 3'-regions include the tobacco ribulose bisphosphate carboxylase small subunit termination region; a gene associated with the Ti-plasmid such as the octopine synthase termination region; the tml termination region; and other 3'- regions known to those skilled in the art. Various components of fatty acid synthesis are located in the chloroplast and/or proplastid organelles. Therefore, it is desirable that the ACC polypeptide be translocated to the specific organelle. Accordingly, DNA coding for a translocation or transit peptide optionally including a processing signal, recognized by the plant host can be included in the construct. The transit peptide, also known as a leader sequence, and processing signal may be derived from gene encoding any plant protein which is expressed in the cytoplasm and translocated to the appropriate organelle. For some applications, the leader sequence can be combined in a DNA construct with a seed specific promoter, for example to increase expression in a target tissue of interest, and for others, the leader sequence can be provided under the regulatory control of a more constitutive transcriptional initiation region. By "transit peptide" is meant a sequence capable of translocating a peptide joined to the transit peptide to a particular organelle. For the most part, the transit peptide is from one plant, but is generally recognized by other plants. Thus, the DNA encoding the transit peptide may be native to or heterologous to the ultimate host in which the chimeric gene is introduced. DNA encoding transit peptides may come from soybean, corn, petunias, tobacco, Brassica, tomato, wheat, pea and the like. The DNA encoding the transit peptide may be the complete transit- peptide encoding sequence including the processing signal or a truncated transit- peptide-encoding sequence lacking from about 1 to 10 codons, or a portion of a codon, from the 3' terminus. In addition, one or more changes may be made in the nature of mutations, deletions or insertion in the transit peptide and processing signal, where such change may provide for convenience in construction by providing for a convenient restriction site, or removing an inconvenient restriction site. The mutations may be conservative or non-conservative, so that the transit peptide may be the same or different from the wild-type transit peptide. An additional peptide segment between the transit peptide and the ACC polypeptide may be useful. Such peptide may be the mature (post-processing) amino-terminal portion of the structural peptide or any other peptide providing the appropriate structure features recognized and needed by the plastid translocation system. When post processing amino acids from the SSU leader sequence are included, it is preferred that no more than 50, preferably no more than 40, and most preferably no more than 30 post processing amino acids are present at the N-terminal of the desired ACC polypeptide. However, use of a seed-specific promoter may be desired to selectively modify Since seed differs from leaf tissue, it may be necessary to use different lengths of RUBISCO mature sequence with the transit sequences, or a different transit sequence altogether may be necessary for greatest benefit. In this regard, it is important to note that gene constructs lacking DNA encoding a transit sequence for organelle targeting also may have value since the ACC enzyme product (malonyl-CoA) also is used in extension of 18-carbon fatty acids into longer molecules in plants such as rapeseed and meadowfoam. These extension reactions take place in the cytoplasm, so targeting to the chloroplast or proplastid organelles is not necessary for such applications. However, use of a seed-specific promoter may be desired to selectively modify malonyl-CoA levels in the plant. In developing the expression cassette, the various fragments comprising the regulatory regions and open reading frame may be subjected to different processing conditions, such as ligation, restriction enzyme digestion, resection, in vitro mutagenesis, primer repair, use of linkers and adapters, and the like. Thus, nucleotide transitions, transversions, insertions, deletions, or the like, may be performed on the DNA which is employed in the regulatory regions and/or open reading frame. The expression cassette thus may be wholly or partially derived from natural sources, and either wholly or partially derived from sources endogenous to the host cell, or exogenous to the host cell. Furthermore, the various DNA constructs (DNA sequences, vectors, plasmids, expression cassettes) of the invention are isolated and/or purified, or synthesized and thus are not "naturally occurring." During the construction of the expression cassette, the various fragments of the DNA usually will be cloned in an appropriate cloning vector, which allows for amplification of the DNA, modification of the DNA or manipulation by joining or removing of sequences, linkers, or the like. Normally, the vectors will be capable of replication in at least a relatively high copy number in E. coli. A number of vectors are readily available for cloning, including such vectors as pBR322, pUC series, M13 series, etc. The cloning vector will have one or more markers which provide for selection of transformants. The markers will normally provide for resistance to cytotoxic agents such as antibiotics, heavy metals, toxins, or the like. Often times, markers are selected which can be detected in a plant host. Where the DNA will be microinjected or propelled into the plant cell, a marker usually is chosen which allows for direct selection of those cells in which the injected DNA has become integrated and functional. By appropriate restriction of the vector and cassette, and as appropriate, modification of the ends, by chewing back or filling in overhangs, to provide for blunt ends by addition of linkers, by tailing, complementary ends can be provided for ligation and joining of the vector to the expression cassette or component thereof. After each manipulation of the DNA in the development of the cassette, the plasmid will be cloned and isolated and, as required, the particular cassette component analyzed as to its sequence to ensure that the proper sequence has been obtained. Depending upon the nature of the manipulation, the desired sequence may be excised from the plasmid and introduced into a different vector or the plasmid may be restricted and the expression cassette component manipulated, as appropriate. The manner of transformation of a prokaryotic cloning host with the various DNA constructs (plasmids and viruses) for cloning is not critical to this invention. Commonly, the expression cassette will be joined to a replication system functional in prokaryotes, particularly E. coli, so as to allow for cloning of the expression cassette for isolation, sequencing, analysis, and the like. In most cases the DNA construct will include one or more markers which may allow for selection in the host(s), the markers usually involving biocide resistance, for example antibiotic resistance; heavy metal resistance; toxin resistance; complementation, providing prototropy to an auxotrophic host; immunity; etc. Conjugation, transduction, transfection or transformation, for example, calcium chloride or phosphate mediated transformation, also may be employed. Depending upon the manner of introduction of the expression construct into the plant, other DNA sequences may be required. As discussed above, various marker sequences may find application. In addition, sequences useful to transformation also may be included. For example, the use of T-DNA for transformation of plant cells has received extensive study and is amply described in Hoekema, The Binary Plant Vector Systems, Offsetdrukkerij Kanters B.V., Alblasserdam, 1985, Chapter V, Knauf et al. , "Genetic Analysis of Host Range Expression by Agrobacterium,' In: Molecular Geneύcs of the Bacteria-Plant Interaction, Puhler, A. ed., Springer- Verlag, NY, 1983, p. 245, and An et al, EMBO J. , (1985) 4:277-284. Conveniently, explants, cotyledons, or other plant tissue may be cultivated with A. tumefaciens or A. rhizogenes to allow for transfer of the expression construct to the plant cells, the plant cells dispersed in an appropriate selective medium for selection, grown to callus, shoots grown and plantlets regenerated from the callus by growing in rooting medium. The Agrobacterium host will contain a plasmid having the vir genes necessary for transfer of the T-DNA to the plant cells and may or may not have T-DNA. If the expression construct is to be inserted into the host cell by injection or electroporation, disarmed Ti-plasmids (lacking the tumor genes, particularly the T- DNA region) may be used. Examples of suitable plant hosts include soybean, sunflower, corn, peanut, maize, cotton, safflower and rapeseed. Other plant hosts which may be used include tomato, strawberries, melons, banana, ornamental plants and the like. Various techniques exist for determining whether the desired DNA sequences present in the plant cell are integrated into the genome and are being transcribed. Techniques such as the Northern blot can be employed for detecting messenger RNA which codes for the ACC polypeptide. In addition, the presence of expression can be detected in a variety of ways, such as assaying for enzyme activity or immunoassay for the protein product. A desired phenotype in this case is increased lipid content in a plant tissue of interest, particularly leaves and seed. By "transformed cell" or "transgenic cell" is meant a cell into which (or an ancestor of said cell) into which by means of recombinant DNA techniques, DNA encoding an ACC polypeptide has been introduced. Plant cells transformed with a plant expression vector can be regenerated, for example, from single cells, callous tissue or leaf disks according to standard plant tissue culture techniques. Transgenic plants expressing a selectable marker, are screened for transmission of the transgene DNA by standard DNA detection techniques. Each positive transgenic plant and its transgenic progeny are unique in comparison to other transgenic plants established with the same transgene. Integration of the transgene DNA into the plant genomic DNA is in most cases random and the site of integration can profoundly affect the levels, and the tissue and development or patterns of transgene expression. Consequently, a number of transgenic lines are usually screened for each transgene to identify and select plants with the most appropriate expression profiles. The cells which have been transformed may be grown into plants in accordance with conventional ways. See, for example, McCormick et al , Plant Cell Reports (1985) 5:81-84. These plants may then be grown, and either self pollinated or cross-pollinated identifying the resulting hybrid having the desired phenotypic characteristic. Two or more generations may be grown to ensure that the subject phenotypic characteristic is stably maintained and inherited and then seeds harvested for use to provide plants having the new phenotypic property expressed in a desired plant tissue, particularly increased lipid levels due to production of lipid synthesis precursors. The subject invention finds use in increasing the level of malonyl-CoA present in a plant cell. Malonyl-CoA is involved in several different plant biosynthetic pathways, therefore an increase of malonyl-CoA levels has a variety of applications. For example, increased malonyl-CoA in leaf tissue increases the lipid content, increased malonyl-CoA in seed tissue may also increase lipid content in such tissues; increased malonyl-CoA in plant fruit tissue (e.g., tomato fruit, cotton ball, rapeseed pod) hastens and/or facilitates fruit abscission by increasing ethylene production; increased malonyl-CoA in the tissues which are capable of producing flavonoids or cuticular waxes results in increased production of these components, leading to modified flavor or increased drought tolerances, respectively. Additionally, BCCP can function as a non-specific CO 2 donor in the plant cell, thus overexpression of the BCCP subunit provides a method for increasing activity of other biotin-containing carboxylases, e.g. 3- methylcrotonylCoA carboxylase (involved in catabolism of leucine), propionylCoA carboxylase (involved in degradation of branched-chain amino acids and odd- numbered fatty acids), and pyruvate carboxylase (for gluconeogenesis and lipogenesis). The following examples are offered by way of illustration and not by limitation. EXAMPLES Example 1 Construction of BCCP gene constructs for expression in leaves. Plasmids pCGN3994, pCGN3995, and pCGN3996 contain the complete coding sequence for the 156 amino acid E. coli BCCP gene, a CaMV 35S promoter, tml 3' transcription termination sequence from the Agrobacterium Ti plasmid for plant expression, and a kanamycin (npt) resistance gene for selection in plants. All three plasmids are derived from pCGN3988, which contains the E. coli accB gene, pCGN3988 is prepared as follows, using the polymerase chain reaction (PCR). The template for the PCR chain reaction is pCGN3916, a Bluescript KS+ plasmid (Stratagene Cloning Systems, La Jolla, CA) containing an approximately 6.5 kb fragment of the E. coli MM294 (ATCC #33625) chromosome that includes αccB and flanking sequences. The PCR reaction as described can be performed using E. coli MM294 genomic DNA as a template rather than pCGN3916. Genomic DNA from E. coli MM294 is isolated as described by Silhavy and Coworkers (Silhavy, et al. , (1984) Experiments with Gene Fusions, Cold Spring Harbor, New York). The complete coding sequence of the E. coli accB contained on pCGN3916 is shown in Fig. 3, and is available in GΕNBANK under the acquisition number M83198. The forward and reverse primers for amplification included restriction endonuclease cleavage sites for BamϊU. and Sacl respectively, and have the following sequences: 5'-CUACUACUACUAGGGGATCCTATGGATATTCGTAAGATT-3' (forward primer), and 5'-CAUCAUCAUCAUGAGCTCTTACTCGATGACGACCAG-3' (reverse primer). PCR reactions were performed using a GeneAmp Kit (Perkin- Εlmer Cetus, Norwalk, CT) and a programmable thermocycler (Perkin-Εlmer Cetus). Amplification was as follows: 15 cycles of 94°C for 1 min, 55°C for 2 min, 72°C for 3 min., 10 cycles of 1 min 94°C, 2 min. at 55°C, and 72°C for 3 min. 15 sec. initially and increasing the time by 15 seconds each cycles such that the last cycle is 5 min. 45 sec. Reactions were performed in a 100 μ\ volume and contained 100 ng supercoiled plasmid DNA as template, 1 μM forward and reverse primer, 0.2 mM of each of the four deoxyribonucleoside triphosphates (dNTP), 50 mM KC1, lOmM Tris-HCl (pH 8.3), 1.5 mM MgCl 2 , 0.01 % gleatin, and 2.5 units of Taq DNA polymerase. The amplified product was cloned into pAMPl using the BRL CloneAmp system (BRL, Gaithersburg, MD) and conditions recommended by the supplier. One clone, the sequence of which was verified as having an exact match with the E. coli accB sequence (Muramatsu and Mizuno, (1989) Nucleic Acids Research 12:3982), was named pCGN3988. Transcriptional regulatory sequences for expression in plants were attached to the E. coli accB in the following manner. The approximately 500 bp Bam l-Sacl insert in pCGN3988 was inserted into similarly cleaved pCGN2187 (see Figure 1) plasmid DNA. In the resulting plasmid, pCGN3989, accB is transcribed from the CaMV d35S promoter and transcription terminates in the tml y sequence downstream of αccB. Additional plant sequences were added to plasmid pCGN3989 to direct the E. coli BCCP to the chloroplast/plastid. Relatively few data are available concerning the optimal amount of targeting sequence necessary for chloroplast/plastid localization. It therefore was necessary to determine this empirically, and constructs were designed that would allow the addition of the transit peptide (TP) from the small subunit of ribulose bisphosphate carboxylase (RUBISCO) from soybean, required for plastid localization, and DNA sequences encoding either 6 or 12 amino terminal amino acids of the mature small subunit (SSU) gene from the pea RUBISCO. Two cloning steps were required. First, Xbal-SaR fragments from BaBl digested derivatives of pCGN1096, pCGNl 113 and pCGNl 119, containing the TP and 6 or 12 amino acids of the mature SSU respectively, were cloned into pCGN566. pCGN566 was prepared as follows. pUC12 (Cm R and pUC13 (Cm R ) (Ken Buckley Ph.D. thesis, U.C. San Diego) were each digested with EcøRI and Hind-U and polylinkers from pUC18 and pUC19 were inserted respectively into the linearized pUC12 and pUC13 to give pCGN565 and pCGN566 respectively. Each of the plasmids carry a chloramphenicol resistance marker. pPMGl l (Comai et al, (1983) Science 221:370) contains a mutated arok gene resistant to glyphosate inhibition as a Sall-HindHl fragment. pPMG was digested with SaR and BgU and inserted into BamYH-SaR digested pACYC184 (Chang and Cohen, (1978) J. Bacteriol 24: 1141) to provide pPMG17, with the arok fragment. pUC9 (Vieira and Messing, (1982) Molecular Cloning Cold Spring Harbor Lab Manual) was partially digested with Accl and pPMG17 partially digested with Hpaϊ to provide an about 1.6kbp fragment which was inserted into the Accl site of pUC9 to provide pPMG31. pPMG31 was digested with Hindm, resected about 150bp with BaBl, Bamϊ . linkers ligated to the linear DNA and the DNA digested with BαmHI and SaR. The resulting fragment carried the arok gene with 8bp of the 5' untranslated region (TGAGTTTC-sense strand). The fragment was inserted into M13mp9 (Messing and Vieira, (1982) Gene 12:269) which had been digested with BamHl and Sail to yield the phage M-13- 65B48 containing the arok gene as a BamHl-SaR fragment. M-13-65B48 was digested with Nαrl and Pstl, generating an arok fragment lacking the DΝA region 5' of the Ncrl site, corresponding to the amino terminal portion of the gene. This fragment was cloned in pUC8 cut with Accl and Pstl, resulting in pPMG58. This plasmid encodes a lac-arok fusion protein in which 11 amino acids of the pUC8 lac alpha gene replace the 14 amino acids of he Ν-terminus of the arok gene. pPMG34 has been described previously (Stalker et al. , (1985) J. Biol Chem. 26 :4724-4728). The BamHl to SaR fragment containing the arok gene was cloned in pUC9, resulting in pPMG34J. Starting from the BamHl site, the 5 '-untranslated region of the arok gene was recessed by treatments with T4 DΝA polymerase in the presence of a single nucleoside triphosphate, followed by mung bean nuclease digestion. After each T4 DΝA Polymerase and mung bean treatment, the fragment was subcloned as a blunt to SaR insert into a pUC vector, and transformants were screened for the expected product. After two of these steps a clone into a pUC18 was isolated in which the first nucleotide of the Met codon was part of an Xbal site (...tctagatg). This plasmid, called pPMG34.2, was cut with Xbal, treated with T4 polymerase in the presence of dGTP, followed by mung bean nuclease, and T4 DΝA ligase. The DΝA was transformed into E. coli LC3, an arok mutant, (Comai et al. , (1983) Nature 111:741-744) and transformants were selected on minimal medium. Several plasmids complementing the arok phenotype were characterized. Plasmid pPMG34.3 was found to carry an arok/ lac fusion in which the first nucleotide of the arok Met codon had been deleted. M-13-65B48 was digested with BamHl and Sail and the resulting BamHl-Sat fragment inserted into the BamHl-SaR site of pCGN565. The resulting plasmid, pPMG63, was first linearized with Xmal, followed by digestion with mung bean nuclease to remove the overhangs, and the resulting fragment ligated to Sphl linkers, followed by digestion with Sphl and Sail. pCGN566 was completely digested at the unique Sphl and Sail sites and the Sphl-Sall fragment containing the arok gene inserted into the site to provide pPMG64 which contains the chloramphenicol resistance gene. ρPMG64 was digested with Sphl and a 0.6kb pCGN330 Sphl fragment inserted into the Sphl site so as to provide the RUBPCssu leader peptide in the proper orientation with the arok gene. The Sphl site is proximal to the 3'- terminus of exon 1 of the RUBPCssu gene. The Sphl and BamHl sequences are separated by a single base pair and provide for the RUBPCssu leader peptide and processing signal in proper reading frame with the arok gene. The sequence is as follows: ...ACAAT I GCATGC | C | GGATCC | CG | TGACTTTC | ATGGAA... Sphl BamHl 5'-UT arok arok coding region region RUBPCss coding | linker region | region The resulting plasmid pPMG70 was digested with HindTD. to remove the upstream untranslated (UT) region of the small subunit to provide plasmid pPMG72. Plasmid pPMG72 was treated with Hitidm and Ecό l, and the SSUorøA promoter/gene fragment was cloned in pSP64 (Melton et al. , (1986) Nucleic Acid Research 12:7035) which had been digested with HinάTR and EcσRI providing plasmid pCGN1068. The vector pSP64 allows in vitro transcription of cloned DNA. This fusion was planned in such a way that 24 amino acids of the mature SSU peptide are present between the small subunit transit peptide and the arok sequence. Plasmid pCGN1068 was cut with Xbal, the resulting stoppered ends were "filled" with the large EcøRI DNA polymerase fragment (Klenow fragment), the plasmid was cut again with Smal and ligated. This caused the loss of a BamHl site present between the Xbol and Smal site. The resulting plasmid pCGN1075 was cut with EcoW and HindBl releasing the SSV-arok chimeric gene (Fusion 1). This gene was cloned in Bluescribe-M13 vector (Vector Cloning Systems, San Diego) cut with EtøRI and HindTΩ. resulting in pCGN1076. Plasmid pCGN1076 was cut with Sphl and BamHl and a 70bp Sph -Seuik fragment from a pea SSU cDNA clone was ligated to pCGN1076 resulting in pCGN1077. Such 70bp Sphl-Seuik fragment was isolated by digesting plasmid pSS15 (G. Corussi et al. , (1983) J. Biol. Chem. 25& 1399) with Seuik and Sphl, separating the resulting fragments by agarose gel electrophoresis and electroelution from the gel. The chimeric gene in pCGN1077 consisted of the transit peptide of the soybean SSU, part of the mature pea SSU (24 amino acids) and the arok gene. The following is the construction scheme: the arok moiety of pCGN1077 was removed by digestion with Sphl and SaR. In its place was cloned the region coding for the mature SSU, as an Sphl and Pstl, and then excising it with Sphl and SaR. The resulting plasmid, pCGN1094, codes for an hybrid SSU having the transit peptide of the soybean clone, and the mature portion of the pea clone and carries Sstl and EcøRI sites 3' of this coding region. The HinάlTL to BamHl region of transposon Tn5 (Jorgensen et al, (1979) Mol. Gen. Genet. 177:65) encoding the kanamycin resistance gene was cloned into the same sites of pBR322 (Bolivar et al. , (1977) Gene 2:95) generating pDS7. The Bgϊl site 3' of the kanamycin resistance gene was digested and filled in with the large fragment of E. coli DNA polymerase 1 and deoxynucleotides triphosphate. An Sstl linker was ligated into the blunted site generating plasmid pCGN1093. Plasmid pPMG34.3 was digested with SaR, the site filled in as above and EcøRI linkers were ligated into the site resulting in plasmid pCGN 1092. The letter plasmid was digested with Sstl and Smal and into it was ligated the kanamycin resistance gene excised from pCGN1093 with Sstl and Smal giving pCGN1095. The kanamycin and arok gene were excised as a piece from pCGN1095 by digestion with Sstl and EcoRI and inserted into the Sstl and EcoKl sites of pCGN1094 giving pCGN1096. Summarizing, pCGN1096 contains 5' to 3' the following pertinent features: The SSU gene - a polylinker coding for Pstl, SaR, Sstl, and Kpnl - the kanamycin resistance gene - Smal and BamHl restriction sites - the arok gene without the original ATG start codon. A description of the use of BaBl chewbacks of pCGN1096, as well as a description of pCGN1096 and pCGN566 may be found in Comai, et al , (1988) J. Biol Chem. 2£&- 15104-15109. This manipulation allowed these fragments subsequently to be cloned as BamHl firagments into the BamHl site of pCGN3989 to yield pCGN3992 and pCGN3993 containing the TP and 6 or 12 amino acids of SSU respectively. Pstl fragments from pCGN3989 (d35S-αccB-/rø 3'), pCGN3992 (d35S- TP-SSU+6 amino acids-αccB-/m/3') and pCGN 3993 (d35S-TP-SSU+ 12 amino acids-αccB-tm 3') were cloned into the Pstl site of pCGN1547 (McBride and Summerfelt, (1990) Plant Molec. Biol. 14:269-276) yielding plasmids pCGN3996, pCGN3995 and pCGN3994. The accB genes in pCGN3996, pCGN3994 and pCGN3995 are transcribed in the same direction as the mas5'-npt-mas3' gene in pCGN1547. Plasmid pCGN1547 is a binary plant transformation vector. Example 2 Construction of BCCP gene constructs for expression in seeds. Seed-specific expression of foreign genes is now a well-established technique involving the use of gene expression cassettes engineered for convenience of inserting a DNA sequence comprising a protein- or antisense- coding region for expression in transgenic plants. The fused transit +6/accB sequences in pCGN3992 can be excised as a Sall-Sacl fragment which can then be adapted to appropriate sticky end or blunt termini to fit into a seed-specific expression cassette. Alternatively, the fused transit +6/accB coding region can be excised by PCR using primers that add useful restriction sites to the termini of the amplified PCR product. Example 3 Expression of ACC subunits: TC and BC Since expression of E. coli BCCP is effective in vivo to increase lipid biosynthesis, it follows that comparable engineering of other E. coli ACC subunits also will be beneficial. Such engineering can be done exactly as performed for accB: the αccA, accC, and accO genes can each be cloned as BamHl-Sacl fragments using appropriate primers for acck, forward and reverse respectively: CUACUACUACUAGGGGATCCTATGAGTCTGAATTTCCTT CAUCAUCAUCAUGAGCTCTTACGCGTAACCGTAGCT For accC: CUACUACUACUAGGGGATCCTATGCTGGATAAAATTGTT CAUCAUCAUCAUGAGCTCTTATTTTTCCTGAAGACC For accO: CUACUACUACUAGGGGATCCTATGAGCTGGATTGAACCA CAUCAUC AUC AUG AGCTCTCAGGCCTCAGGTTCCTG based on published DNA sequences. Constructs then can be made in similar fashion as that described above for accB using gene expression cassettes such as pCGN2187 (see above) or ρCGN3223 (Voelker et al., Science 257:72-74). It may be desirable to express occA and accD in the same plant cell host. In such cases, a large binary cassette can be prepared or two different binaries created and two separate transformation steps performed (either into the same plant tissue or into different tissues which are regenerated and later crossed together). Additional selectable markers be necessary when αccA and accD are desired together. Generation and analyses of transgenic plant materials can be done in an analogous manner. Example 4 Plant Transformation A variety of methods have been developed to insert a DNA sequence of interest into the genome of a plant host to obtain transcription or transcription and translation of the sequence to effect phenotypic changes. Brassica Transformation Seeds of Brassica napus cv. Westar are soaked in 95 % ethanol for 2 min. surface sterilized in a 1.0% solution of sodium hypochlorite containing a drop of Tween 20 for 45 min., and rinsed three times in sterile, distilled water. Seeds are then plated in Magenta boxes with 1/lOth concentration of Murashige minimal organics medium (Gibco; Grand Island, NY) supplemented with pyridoxine (50 μg/1), nicotinic acid (50 μg/1), glycine (200 g/1), and 0.6% Phytagar (Gibco) pH 5.8. Seeds are germinated in a Percival chamber at 22°C in a 16 h photoperiod with cool fluorescent and red light of intensity approximately 65 μ Einsteins per square meter per second (/xEm^S "1 ). Hypocotyls are excised from 5-7 day old seedlings, cut into pieces approximately 4mm in length, and plated on feeder plates (Horsch et al, (1985) Science 227: 1229-1231). Feeder plates are prepared one day before use by plating 1.0 ml. of a tobacco suspension culture onto a petri plate (100x25mm) containing about 30 ml MS sale base (Carolina Biological, Burlington, NC) 100 mg/1 inositol, 1.3 mg/1 thiamine-HCl, 200 g KH 2 PO 4 with 3% sucrose, 2,4-D (l.Omg/1), 0.6 w/v Phytagar, and pH adjusted to 5.8 prior to autoclaving (MS 0/1/0 medium). A sterile filter paper disc (Whatman 3mm) is placed on top of the feeder layer prior to use. Tobacco suspension cultures are subcultured weekly by transfer of 10 ml of culture into 100 ml fresh MS medium as described for the feeder plates with 2,4-D (0.2mg/l), Kinetin (OJmg/1). In experiments where feeder cells are not used hypocotyl explants are cut and placed onto a filter paper disc on top of MSO/1/0 medium. All hypotocol explants are preincubated on feeder plates for 24 h. at 22°C in continuous light of intensity 30 μEm^S" 1 to 65 EM^S "1 . Single colonies of A. tumefaciens strain EHA 101 containing a binary plasmid are transferred to 5ml MG/L broth and growth overnight at 30°C. Hypocotyl explants are immersed in 7- 12ml MG/L broth with bacteria diluted to 1x10* bacteria/ml and after 10-25 min. are placed onto feeder plates. Per liter MG/L broth contains 5g mannitol, lg L-Glutamic acid or lJ5g sodium glutamate, 0.25g kH 2 PO 4 , OJOg NaCI, OJOg MGSO 4 7H 2 O, 1 mg biotin, 5 g tryptone, and 2.5 g yeast extract, and the broth is adjusted to pH 7.0. After 48 hours of co- incubation with Agrobacterium, the hypocotyl explants are transferred to B5 0/1/0 callus induction medium which contains filter sterilized carbenicillin (500mg/l, added after autoclaving) and kanamycin sulfate (Boehringer Mannheim; Indianapolis, IN) at concentrations of 25 mg/1. After 3-7 days in culture at 65 / EM^S "1 continuous light, callus tissue is visible on the cut surface and the hypocotyl explants are transferred tq shoot induction medium, B5BZ (B5 salts and vitamins supplemented with 3mg/l benzylaminopurine, 1 mg/1 zeatin, 1 % sucrose, 0.6% Phytagar and pH adjusted to 5.8). This medium also contains carbenicillin (500 mg/1) and kanamycin sulfate (25 mg/1). Hypotocol explants are subcultured onto fresh shoot induction medium every two weeks. Shoots regenerate from the hypocotyl calli after one to three months. Green shoots at least 1 cm tall are excised from the calli and placed on medium containing B5 salts and vitamins, 1 % sucrose, carbenicillin (300 mg/1), kanamycin sulfate (50 mg/1) and 0.6% w/v Phytagar). After 2-4 weeks shoots which remain green are cut at the base and transferred to Magenta boxes containing root induction medium (B5 salts and vitamins, 1 % sucrose, 2 mg/1 indolebutyric acid, 50 mg/1 kanamycin sulfate and 0.6% Phytagar). Green rooted shoots are tested for kanamycin-resistance enzyme activity. Example 5 Analysis of Transgenic B. Napus Tissues Western analysis. B. napus plants transformed with plasmids pCGN3994, pCGN3995, pCGN3996 and ρCGN1547 were analyzed for expression of the E. coli BCCP using a modification of the Western blotting technique. Leaf discs from transgenic plants were obtained from young leaves using a #12 cork borer; the tissue was frozen immediately in liquid nitrogen to prevent protein degradation. Soluble proteins were extracted from leaf discs as follows. One leaf disc (approx. 50 mg fresh weight) was transferred to a 1.5 ml Εppendorf tube containing 100 μ\ of extraction buffer (100 mM NaHPO 4 (ρH6.8), 150 mM NaCI, 10 mM ΕDTA, 10 mM DTT, 10 mM thiourea, 0.3% Tween-20, 0.05% TritonX- 100). The sample was homogenized 5 min. using an electric grinder, and then centrifuged at 4°C for 5 min. at 16,000 x g to remove insoluble material. The supernatant fraction was saved and 200 μg samples of protein from the supernatant were separated by sodium dodecyl sulfate (SDS)-polyacrylamide gel (PAGE) electrophoresis (12% polyacrylamide) (Laemmli, (1970) Nature (London) 227:680- 685). Proteins were electrophoretically transferred to nitrocellulose (Towbin et al. , (1979) Proc. Natl. Acad. -Sci. USA 7^:4350-4354). The nitrocellulose filter was washed for 2 hrs. with TTBS (50 mM TrisHCl (pH 7.5), 200 mM NaCI, 0.5% Tween-20) containing 1 % (w/v) skim milk to saturate non-specific protein binding sites. Streptavidin conjugated with alkaline-phosphatase (BRL, Gaithersburg, MD) was added to a final concentration of 2 /zg/ml, and the filter was incubated for 4 hrs. at room temperature with constant shaking. The filter was washed four times with TTBS, once with substrate buffer (0J TrisHCl (pH 9.5), 0.1 M NaCI, 50 mM MgClj) and then incubated with substrate buffer containing 0.044 mg/ml nitroblue tetrazolium (BRL, Gaithersburg, MD) and 0.033 mg/ml 5-bromo-4-chloro-3indolylphosphate (BRL, Gaithersburg, MD) to detect biotinylated proteins. Plants transformed with plasmids pCGN3994, pCGN3995, and pCGN3996 contain biotinylated proteins not present in a control plant containing pCGN1547 (Fig. 4), indicating that the E. coli accB is expressed and biotinylated in plants. The largest of the new proteins in extracts from pCGN3994, pCGN3995, and pCGN3996 are 23 kDa, 21 kDa, and 22 kDa respectively, which are consistent with the observed molecular weight of the E. coli BCCP, 22 kDa (Li and Cronan, (1992) J. Biol. Chem. 261: 16841-16847). Analysis of leaf lipids. Plants were analyzed for changes in fatty acid content and composition using a modification of the method of Browse and coworkers (Browse et al, (1986) Anal. Biochem. 122: 141-145). Leaf discs (approx. 200 mg dried wt) punched from B. napus leaves were frozen immediately in liquid nitrogen, lyophilized, and then placed in 15 ml screw-capped glass tubes with teflon caps. After addition of 4 ml of methanolic H 2 SO 4 reagent (5% w/v H 2 SO 4 in ethanol), and 0.25 ml heptadecanoic (17:0) acid (1 mg/ml toluene), the samples were heated for 2 hrs at 90°C, and then cooled at room temperature. 4 ml of 0.9% (w/v) NaCI and 1 ml of hexane were added, and the samples were shaken briefly to extract fatty acid methyl esters into the hexane phase. Samples were centrifuged (1000 x g for 1 min) to completely separate the phases, and aliquots (1-2 μ\) of the hexane phase was analyzed by gas chromatography. Analysis of fatty acid composition of lipids from B. napus leaves is shown in Table 1 (below). Samples 1547-1 and -4 represent transgenic control plants containing no αccB constructs. Samples prefixed with 3994, 3995, ad 3996 refer to transgenic rapeseed plants resulting from co-cultivations with Agrobacterium strains containing pCGN3394, pCGN3995, and pCGN3996 respectively. The suffix number (i.e., -10 for sample 3994-10) refers to a specific and unique transformation event. Leaf lipid is expressed as total fatty acids as a percent of dry weight; other percent figures represent relative amounts of major fatty acids found in leaf tissue. Transgenic plants 3995-1, -2, -3 all had unusually high total leaf lipids as well as elevated palmitate levels (C16:0) when compared to controls and other transgenic plants. Event 3995-7 does not appear different than controls; this is apparently due to this transformation event being a relatively poor expressor of the αccB gene construct. Table 1 Fattv Acid Composition of Lipids from B. NODUS Leaves As shown in Table 1, three of four independently transformed plants containing pCGN3995 were found to have nearly 2-fold higher amounts of lipids than control plants containing pCGN1547. Plants transformed with pCGN3996 or pCGN3994 had a lipid composition indistinguishable from control plants. These data suggest that the amount of mature SSU is critical for proper expression of the £. coli BCCP and that expression of that protein in the cytoplasm (pCGN3996 plants) does not affect the fatty acid biosynthetic pathway in leaf tissue. In this invention, we demonstrate that expression of an E. coli encoding BCCP in transgenic plants can enhance lipid biosynthesis. The gene product, even though it derives from a prokaryotic source, is correctly biotinylated by the plant cell, and apparently interacts with the plant enzyme to increase malonyl-CoA levels and therefore flux through the fatty acid biosynthetic pathway. The enhancement of fatty acid biosynthesis is observed only with gene constructs that contain transit sequences designed to target the biotinylated BCCP to the chloroplast compartment. However, malonyl-CoA is involved in biosynthesis pathways found in the plant cytoplasm. The combination of this new knowledge relating to enhancement of fatty acid biosynthesis with existing seed-specific gene expression control sequences directly allows the use of BCCP or other E. coli ACC subunit genes to be used in transgenic plants to effect increased levels of malonyl-CoA and to increase lipid biosynthesis in oilseed crops. Heretofore, it has not been possible to increase the amount of malonyl- CoA in a plant cell. Regardless of the means used to increase malonyl-CoA, the above noted effects, particularly increases in lipid content, are desirable and possible. Also, as described, increased malonyl-CoA in a target tissue and/or target organelle of interest can be used to further direct and control effects of increased malonyl-CoA. Importantly, it is now discovered that increased malonyl- CoA in plant tissues generally does not appear to affect plant vitality. Thus, by this invention, production of lipids can be controlled so as to provide a means not only to increase oil yield in seed, but also to increase fruit abscission as a result of increased ethylene production, to increase drought tolerance as a result of increased cuticular wax production, to modify colors influenced by flavonoids and to increase resistance to certain plant pests as a result of increased expression of malonylCo-A-derived phytotoxins in a variety of tissues particularly leaf, fruit and root. All publications and patent applications mentioned in this specification are indicative of the level of skill of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. The invention now being fully described, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the appended claims.

Claims: WHAT IS CLAIMED IS: 1. A method of increasing lipid levels in plant tissue, said method comprising: increasing the amount of malonyl-CoA present in chloroplast or proplastid organelles of said plant tissue during lipid biosynthesis. 2. A method of increasing lipid levels in plant tissue, said method comprising: increasing the amount of an ACC polypeptide in chloroplast or proplastid organelles of said plant tissue during lipid biosynthesis, whereby malonyl-CoA metabolization is increased and lipid levels in said plant tissue are increased. 3. The method according to Claim 2, wherein said ACC polypeptide is encoded by DNA obtainable from a prokaryotic genome. 4. A method of increasing the amount of malonyl-CoA present in a plant cell, said method comprising: growing a transgenic plant cell or a progeny cell of said transgenic plant cell comprising an expression construct, said expression construct comprising, in the direction of transcription as functionally linked components, a transcriptional and translational initiation region functional in a plant cell, first DNA encoding an ACC polypeptide, and a transcriptional termination region functional in a plant cell, wherein said DNA is obtainable from a prokaryotic organism. 5. A nucleic acid construct comprising: in the direction of transcription as functionally linked components, a transcriptional and translational initiation region functional in a plant cell, DNA encoding an ACC polypeptide, and a transcriptional termination region functional in a plant cell, wherein said DNA is obtainable from a prokaryotic genome. 6. The nucleic acid construct according to Claim 5, wherein said prokaryotic genome is an E. coli genome. 7. The nucleic acid construct according to Claim 5, wherein said ACC polypeptide is BCCP. 8. The nucleic acid construct according to Claim 5, wherein said ACC polypeptide is E. coli BCCP. 9. The nucleic acid construct according to ' Claim 5, wherein said transcriptional and translational initiation region comprises a double CaMV 35S promoter. 10. The nucleic acid construct according to Claim 5, wherein said transcriptional and translational initiation region comprises a promoter preferentially expressed in one or more specific plant tissues. 11. The nucleic construct according to Claim 10, wherein said specific plant tissues are selected from the group consisting of leaf, seed, fruit and root. 12. The nucleic acid construct according to Claim 5, further comprising operably linked second DNA encoding a translocation peptide which permits transfer of said ACC polypeptide to a chloroplast or proplastid organelle. 13. The nucleic acid construct according to Claim 12, wherein said translocation peptide is all or a portion of a transit peptide of the small subunit of ribulose-1 , 5-bisphosphate carboxylase. 14. The nucleic acid construct according to Claim 13, further comprising operably linked third DNA encoding post-processing amino acids of said ACC polypeptide . 15. A plant cell comprising a nucleic acid construct according to Claim 5. 16. A transgenic plant cell comprising a prokaryotic ACC polypeptide. 17. A plant cell wherein lipid levels have been increased by the method of Claim 1. 18. The plant cell according to Claim 17, wherein said plant cell is a seed cell or a leaf cell. 19. A method of producing an ACC polypeptide in a plant cell, said method comprising: growing a transgenic host cell or a progeny cell of said transgenic host ceil comprising a construct of Claim 5 under conditions whereby said ACC polypeptide is produced. 20. The method of Claim 19, wherein said plant cell is in vivo. 21. A transgenic plant, seed, cell or other plant part comprising: a nucleic acid construct according to Claim 5. 22. A peptide comprising a first peptide region consisting of a transit peptide and processing signal and a second peptide region comprising a prokaryotic ACC polypeptide, wherein said transit peptide permits transfer of said ACC polypeptide to a chloroplast.

Inventors: BEST ELAINE, KNAUF VIC, BEST, ELAINE, KNAUF, VIC
Applicants: CALGENE INC, CALGENE, INC.
Application year: 1994
Main classification: C12N15
IPC codes: C07K14, C11B1, C12N9, C12N15